The present invention relates to a piezoelectric laminate including a potassium sodium niobate layer, and a surface acoustic wave device, a thin-film piezoelectric resonator, and a piezoelectric actuator including the piezoelectric laminate.
A demand for a surface acoustic wave device has rapidly increased along with a remarkable development in the communication field represented by mobile communication such as a portable telephone. The development of the surface acoustic wave device has been trending toward a reduction in size and an increase in efficiency and frequency. This requires a higher electromechanical coupling factor (coefficient) (k2), more stable temperature properties, and a higher surface acoustic wave propagation velocity.
A surface acoustic wave device has been mainly used which has a structure in which interdigital transducers are formed on a piezoelectric single crystal. As typical examples of the piezoelectric single crystal, a rock crystal, lithium niobate (LiNbO3), lithium tantalate (LiTaO3), and the like can be given. For example, LiNbO3 with a high electromechanical coupling factor is used for an RF filter for which an increase in band and a decrease in loss in the passband are required. A rock crystal with a small temperature coefficient of frequency is used for an IF filter for which stable temperature properties are required in a narrow band. LiTaO3 with an electromechanical coupling factor and a temperature coefficient of frequency between those of LiNbO3 and a rock crystal plays an intermediate role between LiNbO3 and a rock crystal. In recent years, a cut angle of a potassium niobate (KNbO3) single crystal showing a high electromechanical coupling factor has been found. A KNbO3 single crystal plate is disclosed in JP-A-10-65488.
In a surface acoustic wave device using a piezoelectric single crystal base, properties such as the electromechanical coupling factor, temperature coefficient, and speed of sound are specific to the material and determined by the cut angle and the propagation direction. For example, a 0°Y-X KNbO3 single crystal base has an excellent electromechanical coupling factor, but does not show zero temperature properties at or near room temperature, differing from a 45° to 75° rotated Y-X KNbO3 single crystal base.